The albumin-creatinine ratio (ACR) assay simultaneously measures two analytes in urine, albumin and creatinine. When the body is functioning properly, albumin is not normally present in urine because it is retained in the bloodstream by action of the kidneys. When small amounts of albumin are excreted into urine from the kidney, a condition called microalbuminuria is present. Microalbuminuria occurs when there is an abnormal leakage of albumin from the kidneys into urine.
Creatinine is a byproduct of creatine phosphate in muscle. In a normal functioning body, it is excreted into urine at a constant rate. When albumin is measured simultaneously with creatinine, the result is known as the albumin-creatinine ratio. The use of ACR for determination of albumin in the urine corrects for the concentration of urine due to varying diuretic output and the hydration status of the patient.
Microalbuminuria in individuals with diabetes or hypertension has shown to be associated with increased risks of developing neuropathy, cardiovascular disease (CVD), retinopathy, preeclampsia, inflammatory conditions, and mortality. The ACR assay serves as an early detection method for kidney damage as well as a monitoring method of treatment efficacy. The ACR assay is frequently used in patients with chronic diseases such as diabetes and hypertension that are at an increased risk of developing kidney failure.
Existing methods for creatinine measurement include colorimetric assays including a chemical method based on Jaffe's reaction, which uses alkaline picric acid, and an enzymatic method by which creatinine is converted with creatinase, and color intensity generated by a peroxidase and a reactive substrate is measured.
Albumin in urine is measured by one of four methods including a colorimetric method by which a dye reacts directly with the albumin molecule to form a colored albumin-dye complex, or immunological methods which uses nephelometry or turbidimetry, and competitive or sandwich immunoassays based on labeled antibodies.
Current methodologies for performing tests for albumin-creatinine ratio are complex to perform or require expensive instrumentation and are generally performed in clinical laboratories. It would be advantageous to develop a simplified assay that can be a point-of-care or an over-the-counter product.